Anode, process for anodizing, anodized wire and electric device comprising such anodized wire

ABSTRACT

An anode, process for anodizing, an anodized wire and electric device having an anodized wire for use in high-voltage electric machines. A predetermined length of metallic conductor wire is wound around a holder, where respective windings are separated from one another with guide cams and guide slots. The metallic conductor wire and holder are then disposed in an electrolyte, where both ends of the metallic conductor wire are connected to a positive pole on a current source so as to implement the anodization operation. An oxide layer is formed as a result of the anodizing operation on a metallic portion of the metallic conductor wire. Properties of the oxide layer are such that the electrical insulation properties and adherence of the oxide layer to the wire are suitable for use in windings of electric machines for high-voltage applications.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an anode for batch anodizing of a length ofmetallic conductor wire. More specifically, the invention relates to ananode for generating an electrically insulating oxide layer on thesurface of a wire length of electric conductor wire of metal byanodizing, wherein the anode is immersed into an electrolyte. Theinvention also relates to a process for batch anodizing of a wire lengthof metallic conductor wire, in which such an anode is utilized, aninsulated conductor wire with an electrically insulating surface layerby batch anodizing according to the invented anodizing process, and anelectric device having one or more such insulated conductor wires whichhave been provided with an electrically insulating surface layer bybatch anodizing.

2. Discussion of the Background

An electric device such as a cable, a transformer, a generator, a motor,etc., has at least one current carrying and voltage-carrying metallicbody, hereinafter in this document referred to as a conductor. Certainhigh-voltage electric devices include conductors which have a largenumber of conductor wires of a more slender dimension, referred to inthis document as strands. The strands are composed, for example laid,into parts of strands, windings or coils in generators and otherelectric machines. The voltage difference between the laid strands islow but the laid strands are still often insulated relative to oneanother.

According to the prior art, single-wire conductor wires which, asstrands, are laid into coarser conductors, included in high-voltagedevices, are insulated preferably by organic insulating materials, suchas thermoplastic resins, waxes or varnishes. However, organic insulatingmaterials have a poor capacity to withstand influence in severeenvironments. For example, they have a low temperature resistance andthey must often be applied in relatively thick layers. The organicinsulations also give rise to drawbacks and costs whenrecycling/recovering consumed or rejected conductor material since theyhave to be taken care of or destructed separately from the metallicconductor wire. For use in severe environments such as at hightemperatures, under vacuum, in chemically aggressive environments or inenvironments involving a high fire hazard, it is known to use inorganicinsulating materials such as insulating materials based on glass fibreor mica, which are usually wound onto the conductor wire. Further, it isknown to insulate aluminum wire or aluminum-coated copper wire with asurface layer of aluminum oxide by anodic oxidation, anodizing. Toobtain an oxide layer with a suitable structure and adhesion for the usedescribed above, a treatment cycle is required which cannot be realizedby way of a continuous electrochemical process but requires a batchprocess. A problem in this connection is to arrange a wire of a wirelength sufficient for a coil- in an electric high-voltage device. Thewire length in a coil usually amounts to between a few two hundredmeters and a few kilometers. The wire must in its entirety be connectedto the positive pole of a current source in such a way that thepotential difference is minimized over the long wire length. The wire,which preferably has a diameter of 1 to 5 mm, must usually be supportedand kept in such a way that essentially the whole surface may beanodized.

SUMMARY OF THE INVENTION

It is an object of the invention to suggest an anode which has a holdersuitable for anodizing, in one batch, a conductor wire with a wirelength of 100 meters to 10 kilometers.

It is also an object of the invention to suggest an anodizing processfor batch anodizing of a conductor wire, an anodized conductor wiremanufactured by way of this process, as well as an electric devicehaving one or more such anodized wires.

The above is achieved by way of an anode which is adapted for batchanodizing of a wire length, includes the wire to be anodized and aholder for supporting and holding the conductor wire, during theanodizing, in such a way that essentially the whole surface of theconductor wire can be anodized, whereby, according to the invention, thewire is spirally wound onto the holder and the holder has at least threeguide cams with guide slots in which the spirally wound wire is fixed.Preferably, the guide slots are formed such that the contact surfacesbetween the holder and the wire are minimized essentially into pointcontacts. The guide slots of the guide cams hold the spiraled conductorwire such that all the turns are separated by a space. By this spacebetween each turn and by the contact surfaces between holder and wirehaving been minimized, it is ensured that essentially the whole envelopesurface of the conductor wire is anodized and that a homogeneous oxidelayer is generated. The wire and the holder are immersed into anelectrolyte during the anodizing, and the wire is connected at both itsends to the positive pole of a current source. The wire includes, atleast in an outer layer, aluminum or copper which during the anodizingis oxidized into an oxide layer with good adhesion, a suitable structureand a thickness of less than 15 μm, preferably less than 10 μm. Thisensures the workability without the oxide layer being damaged or flakedand a sufficient electrical insulation for the limited potentialdifference between two strands included in the same winding or coil in ahigh-voltage electric machine. In certain embodiments, the wire is asolid wire of some of these metals or of an alloy based on aluminum orcopper, and in other embodiments a wire with a core of a first metal oralloy coated with a layer including aluminum or copper; the core may, ofcourse, include aluminum or copper. That is to say, a core of aluminummay be coated with a copper layer, a core of copper with an aluminumlayer or a core of copper or aluminum be coated with an alloy comprisingcopper and aluminum, respectively, where the content of the coatingdiffers from the content of the core. Preferably, during anodizing of abatch of metal wire, a conductor wire with a wire length of 100 metersto 10 kilometers is wound onto the holder. The invention has proved tobe exceedingly suitable for anodizing conductor wire with a diameter of0.1 to 6 mm, preferably 1 to 5 mm.

The guide cams are preferably made of an electrically conductingmaterial such as aluminum, copper or titanium. Under certain conditions,it is also suitable to connect both holder and wire ends to the positivepole of the current source.

In a preferred embodiment, the holder includes a central shaft and threebars, oriented parallel to the shaft and fixed to the central shaft byway of radially oriented arms. The bars are arranged with guide slots orwith guide cams fixed to the bars.

An anode as described above is preferably suitable for use during abatch anodizing where the electrochemical, thermal or other parametersare varied during the process cycle, or during a batch anodizing whichgoes on for such a long time that a process where the wire iscontinuously drawn through the anodizing bath is not suitable.

Depending on the electrochemical conditions prevailing in theelectrolytic bath, either the whole holder is made of an electricallyconducting material and connected as an anode to the positive pole ofthe current source, or only the guide cams fixed to the bars are made ofan electrically conducting material and connected as an anode to thepositive pole of the current source. In the latter case, the guide camsare electrically insulated from the supporting parts of the holder. Theelectrolyte may contain other metal ions or anions, which during theoxidation are included in the oxide layer and act in a stabilizing waythereon or improve the adhesion to the underlying metal or in certaincases change the surface properties of the oxidized conductor wire,which surface properties facilitate water rejection, the application ofpolymer-based surface layers outside oxide layers, etc. The contents ofsuch additives to the electrolyte may be controlled during theanodizing. Alternatively, other electrochemical process parameters,which influence the inclusion of such compounds in the oxide layer, maybe controlled.

Through the anode and the batch anodizing, described above, it ispossible to anodize conductor wires of copper or aluminum or conductorwires coated with any of these metals, such as aluminum-coated copperwires with an electrically insulating oxide layer, which exhibits anadhesion and structure such that they may be treated and formed intocoils or windings in a high-voltage electric machine. The adhesion andthe structure ensure that the electrical insulation may be achieved witha thin oxide layer, which makes them suitable to use as strands in coilsand windings for electric high-voltage devices. It is particularlyadvantageous to use the anode and the anodizing process mentioned abovefor anodizing strands which are coordinated into an electric conductorwhich is wholly or partially surrounded by a polymer-based insulationand arranged to be included in a winding of a high-voltage electricmachine.

A conductor wire according to the invention, as well as a high-voltageelectric machine having such a conductor wire, has an improved poorcapacity of resisting the influence of severe environments. For example,they have a high temperature resistance and may be applied in relativelythin layers. Nor do they give rise to any drawbacks or costs duringrecycling/recovery of consumed or rejected conductor material since theinsulation may be taken care of and destructed together with themetallic conductor wire.

In the following, the invention will be explained in greater detail andbe exemplified by means of a preferred embodiment with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

the invention will now be described in more detail in the followingdescription of preferred embodiments, with reference to the accompanyingdrawings in which:

FIG. 1 is a perspective view of an anode on a holder according to thepresent invention; and

FIG. 2 is a partial view of a cam with wire therearound according to thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, the anode in FIG. 1 includes a holder inthe form of a central shaft 1 and three bars 2, 2 a, 2 b, 2 c, arrangedparallel to the shaft and fixed to the central shaft by way of radiallyoriented arms 3 a, 3 b, 3 c. On the bars 2, 2 a, 2 b, 2 c, guide cams 4,4 a, 4 b, 4 c are fixed. The guide cams 4, 4 a, 4 b, 4 c are made ofaluminum and are shown in more detail in FIG. 2. The guide cams 4, 4 a,4 b, 4 c may be electrically insulated from the supporting parts 2, 2 a,2 b, 2 c, 3 a, 3 b, 3 c of the holder. The wire 5 which is to beanodized is spirally wound onto the holder and each turn is fixed in theguide slots of the guide cams 4 a, 4 b, 4 c. At both ends the wire 5 iselectrically connected to the positive pole of a current source (notshown). During anodizing, the whole holder with the wound-on wire 5 isimmersed into an electrolyte, an electrolytic bath. In the electrolyticbath, the electrochemical, thermal or other parameters are controlledduring the process cycle. In certain cases, the process cycle during thebatch anodizing takes such a long time that, even if the processparameters are kept essentially constant during the whole anodizing, aprocess where the wire is continuously drawn through the anodizing bathis not suitable. Depending on the electrochemical conditions prevailingin the electrolytic bath, either the whole holder is made of anelectrically conducting material and connected as an anode to thepositive pole of the current source, or only the guide cams 4 a, 4 b, 4c, fixed to the bars, are made of an electrically conducting materialand connected as an anode to the positive pole of the current source. Inthe latter case, the guide cams 4 a, 4 b, 4 c are electrically insulatedfrom the supporting parts of the holder. The electrolyte may containother metal ions or anions, which, during the oxidation, are included inthe oxide layer and act in a stabilizing manner thereon, or improve theadhesion to the underlying metal or, in certain cases, change thesurface properties of the oxidized conductor wire, which propertiesfacilitate water rejection, the application of polymer-based surfacelayers outside oxide layers, etc. The contents of such additives to theelectrolyte may be controlled during the anodizing. Alternatively, otherelectrochemical process parameters, which influence the inclusion ofsuch compounds in the oxide layer, may be controlled. By way of an anodeaccording to FIGS. 1 and 2, the batch anodizing may be carried out and athin oxide layer, less than 10 μm, with good adhesion to the underlyingmetal and a suitable structure be generated on conductor wires of copperor aluminum or conductor wires coated with any of these metals such as aaluminum-coated copper wires with an electrically insulating oxidelayer. Since the oxide layer exhibits a good adhesion and a suitablestructure, the conductor wires may be treated and formed into coils orwindings in a high-voltage machine without the electrical insulatingcapacity being reduced by cracks or flaking. This fact, and the smallthickness of the oxide layer, contribute to the conductor wiresaccording to the present invention being very suitable to use as strandsin coils and windings for electric high-voltage devices. It isespecially advantageous to use the anode and the anodizing process,described in the foregoing, for anodizing strands which are coordinatedinto an electric conductor which is wholly or partially surrounded by apolymer-based insulation and is adapted to form part of a winding of ahigh-voltage electric machine. A conductor wire according to theinvention, as well as a high-voltage electric machine with such aconductor wire, have an improved ability to resist the influence ofsevere environments. For example, they have a high temperatureresistance and may be applied in relatively thin layers. Nor does thisgive rise to any drawbacks or costs during recycling/recovery ofconsumed or rejected conductor material since the insulation may betaken care of and be destructed together with the metallic conductorwire.

What is claimed is:
 1. A batch anodization device for anodizing ametallic conductor wire having a predetermined length, comprising: aholder configured to support and hold the metallic conductor wire atcontact points in a predetermined position during an anodizingoperation, said holder including at least three cam guides each havingguide slots, said metallic conductor wire being spirally wound in theguide slots so as to be fixedly held, a separation space betweenrespective of the guide slots in each turn being a predetermineddistance, said holder with said metallic conductor wire configured to beimmersed in an electrolyte during said anodizing operation; and acurrent source having a positive pole, respective ends of said metallicconductor wire connected to the positive pole of the current sourceduring said anodizing operation, wherein said holder including a centralshaft and three bars arranged parallel to the central shaft and fixed tothe central shaft by radially oriented arms.
 2. The anode of claim 1,wherein: the at least three guide cams being made of an electricallyconducting material.
 3. The anode of claim 2, wherein: respective of theat least three guide cams being connected to the positive pole of thecurrent source.
 4. The anode of claim 1, wherein: said metallicconductor wire comprising aluminum.
 5. The anode of claim 1, wherein:said metallic conductor wire including copper.
 6. A method for anodizinga metallic conductor wire having a predetermined wire length, comprisingsteps of: spirally winding said metallic conductor wire onto a holderhaving at least three guide cams with guide slots, including spirallywinding the metallic conductor wire on the holder to form turns that arefixed held at contact points by the guide slots such that the turns ofthe metallic conductor wire being spaced apart by a predetermineddistance, said holder having a central shaft and bars arranged inparallel to the central shaft, the bars being connected to the centralshaft by radially oriented arms; connecting both ends of said metallicconductor wire to a positive pole of a current source; and immersingsaid metallic conductor wire on said holder into an electrolyte.
 7. Themethod of claim 6, further comprising: varying at least one processparameter during the anodizing operation for generating an oxide layerthat fixedly adheres to an underlying metal portion of said metallicconductor wire, said oxide layer having a thickness less than 15 μm. 8.The process of claim 7, wherein: said varying step includes controllingan electrochemical process parameter according to a predetermined cycleduring the anodizing operation.
 9. The process of claim 7, wherein: saidvarying step includes varying a temperature during the anodizingoperation.
 10. An anodized conductor wire comprising: a metallicconductor wire having a predetermined length; an oxide layer disposed onsaid metallic conductor wire by batch anodizing of the metallicconductor wire, said oxide layer being thin and exhibiting a structureand adhesion to an underlying metal portion of said metallic conductorwire so as to be configured for continued adhesion to the underlyingmetal portion when said metallic conductor wire being shaped for use inat least one of a coil and a winding of a high-voltage electric machine;said oxide layer having an electrically insulating property configuredto electrically insulate respective strands of a winding in thehigh-voltage electric machine, wherein said oxide layer being formed bybatch anodizing when said metallic conductor wire being wound on aholder having at least three cam guides with guide slots, a centralshaft and bars arranged in parallel to the central shaft and fixed tothe central shaft by radially oriented arms, contact surfaces betweensaid holder and said metallic conductor wire being contact points, saidguide slots separating respective turns of said metallic conductor wirewhen spirally wound and immersed into an electrolyte and when both endsof said metallic conductor wire being connected to a positive pole of acurrent source.
 11. The anodized conductor wire of claim 10, wherein:said oxide layer being less than 15 μm.
 12. The anodized conductor wireof claim 10, wherein: said metallic conductor wire comprising aluminum.13. The anodized conductor wire of claim 10, wherein: said metallicconduct wire comprising copper.